Personal Genetics Education Project

In the News: First report of baby born with mitochondrial replacement

As researchers, ethicists, policymakers and the broader public continue to debate whether gene editing should be used to modify human embryos, another procedure that would result in genetic changes being passed on to future generations (a situation called “germline genetic modification”) seems to have moved forward.

It was reported this week that the first baby who has undergone the process of “mitochondrial replacement” was born in Mexico in April 2016. A team of American doctors completed the procedure for a couple from Jordan. The baby seems to be healthy so far. It is important to note that, as yet, the medical team’s claim has not been independently verified.

Mitochondria, often called the “power plants” of the cell, play a major role in producing the energy that our cells need to function. Mitochondria actually contain small amounts of their own DNA (the majority of our DNA is located in the cell nucleus; each of our cells’ nucleus contains more than 300 thousand times more DNA than each mitochondrion, but there can be anywhere from tens to thousands of mitochondria per cell). Genetic mutations in mitochondrial DNA are known to cause a number of hereditary diseases, with symptoms ranging from mild to fatal.

Because an individual’s mitochondria normally are only inherited from their mother, a possible way to treat diseases caused by mitochondrial DNA mutations is to replace the mitochondria in an egg cell before using in vitro fertilization (IVF) to conceive a baby. This involves taking the nucleus from the mother’s egg, then placing it into a donor’s egg that has its nucleus removed. A baby born this way will inherit DNA from three people – the father’s sperm, the mother’s egg nucleus, and the donor’s egg mitochondria – giving rise to popular terms such as “three-parent baby”. And because subsequent offspring of the child will inherit the donated mitochondria (along with their small, but important, contribution of DNA), mitochondrial replacement therapy is considered a form of germline genetic modification.

Given the ethical controversies surrounding germline modification and babies born with three people’s DNA, many countries are grappling with how to regulate mitochondrial replacement. Moreover, some scientists have expressed concerns that there are still unknown risks to the procedure, since mitochondria do more than just producing the cell’s energy, and the procedure cannot completely get rid of all the mitochondria from the original egg. In 2015, after many years of public debate and consultation, the United Kingdom became the first country to approve the use of mitochondrial replacement therapy. In the United States, the procedure is not illegal, but any clinical use would require approval by the Food and Drug Administration, which is currently prohibited by Congress to do so. An expert panel convened by the National Academies recommended in February 2016 that mitochondrial replacement be allowed, but only for male embryos – because a male’s sperms do not pass on mitochondria to any future offspring.

The Jordanian couple in the current story, in which the wife carries mitochondrial DNA mutations for a disease called Leigh syndrome, opted for mitochondrial replacement therapy after several failed pregnancies. By using a male embryo for the procedure, the American medical team avoided the issue of germline modification. Some researchers hope that the successful birth of a healthy baby will help convince skeptics of the viability of this procedure. Others, however, are critical of what seems to be a deliberate choice by the medical team to perform the procedure in a foreign country with less clear-cut regulations. The leader of the medical team, who only this year published results from experiments conducted in China in 2003 that involved the same procedure (during which the embryos miscarried), told reporters that, “To save lives is the ethical thing to do.”

Like Louise Brown (the first “test-tube baby” born from IVF), the world will likely be following this baby boy’s life with interest, while the US and other countries continue to wrestle with whether or how to move forward with this potentially life-saving, but ethically controversial, procedure.